This invention relates to an electronic control device for motor vehicle use, and more particularly to determination as to whether or not a duty-driven solenoid valve and its drive circuit are out of order.
In general, with an electronic control device for motor vehicle engine use, as disclosed by Japanese Patent Application Publication No 13102/1986 or 26082/1986, the control duties of solenoid valves adapted to adjust the quantity of air bypassing the throttle valve and the EGR data are calculated according to data such as the quantity of intake air and the number of revolutions per minutes of the engine, and the solenoid valves are controlled according to the control duties thus calculated.
In an electronic control device of this type, an air cleaner is provided upstream of an air intake passageway connected to an engine, and an air flow sensor, an air temperature sensor and a throttle valve are provided in place downstream of the air cleaner. The throttle valve is provided with a throttle degree-of-opening sensor for detecting the degree of opening of the throttle. A bypass passageway is connected to the air intake passageway to bypass the throttle valve. A solenoid valve is connected to the bypass passageway at the middle so as to adjust the quantity of air flowing in the bypass passageway. A surge tank is provided downstream of the throttle valve in the air intake passageway, and an intake manifold is provided downstream of the surge tank. Injectors are provided near the suction ports of the cylinders of the engine. Furthermore, suction valves are provided for the cylinders of the engine. A water temperature sensor is provided for a cooling water passageway which is provided around the cylinders. The intake manifold is coupled through an exhaust gas circulating passageway to an exhaust passageway. An EGR valve is connected to the exhaust gas circulating passageway. A speed change position controlling solenoid valve is provided for a transmission gear coupled to the engine.
The device has a control unit receives the output signals of the above-described air flow sensor, throttle degree-of-opening sensor, air temperature sensor and water temperature sensor. The control unit further receives the output signals of a crank angle sensor mounted on the distributor, and a neutral position detecting sensor for detecting the no-load of the engine, and the output signals of a turbine sensor mounted on the transmission gear, a vehicle speed sensor, and a shift switch for detecting a shift lever's selection range. The control unit calculates fuel injection data, bypass air adjustment data and EGR data mainly according to the output signals of the air flow sensor, the crank angle sensor, the water temperature sensor and the air temperature sensor, and turns on and off or duty-drives the injector, the bypass air adjusting solenoid valve, and the EGR valve according to the data thus calculated.
The control unit selects a most suitable speed change position according to the output signals of the throttle degree-of-opening sensor, the turbine sensor, the vehicle speed sensor and the shift switch, and applies a pulse signal to the speed change position controlling solenoid valve to turn on and off or duty-drives the latter so that the speed change position thus selected be taken quickly.
In the duty drive of each of the above-described solenoids, a timer (particularly a PWM (pulse width modulation) timer) is employed, which is provided inside or outside of a CPU built in the control unit. The employment of the timer results in the advantage that the duty control can be achieved independently of the execution of program by the CPU, and therefore the load applied to the CPU can be decreased as much, and the duty control can be performed with high accuracy.
If, in the above-described electronic control device, the solenoid valve and its drive circuit become out of order, then the exhaust gas may be deteriorated, or running the motor vehicle may become difficult, or the speed change position may be unstable. Accordingly, it is essential to detect the failure of the solenoid valve and the drive circuit, to perform a failsafe operation. That is, it is necessary to monitor the state of the solenoid valve at all times. For this purpose, a method may be employed in which an interruption is carried out whenever the timer for duty-driving the solenoid valve turns on or off the solenoid, to determine whether or not the solenoid valve operates correctly.
However, this failure detecting method gives rise to another problem that a great load is applied to the CPU. In the case where the above-described PWM timer is employed, generally the CPU is not so designed as to perform the interruption with the above-described timing, and therefore it is rather difficult to determine whether or not the solenoid valve and the drive circuit are out of order.